1. Field of the Invention
This invention involves delivering photographic paper to a printer and cutting sheets from an advanced web of the photographic paper so that the sheets can be imaged in the printer and processed to produce prints.
2. Description of the Prior Art
A photographic printer capable of producing different sized prints from a photographic negative preferably has photographic paper delivered from a continuous web that is cut to the desired size sheet for each print. Thebault U.S. Pat. No. 4,547,065 suggests such a printer in which an advanced length of a paper web is imaged and then cut off to drop into a paper processor. The Thebault device advances the paper web downwardly over a fixed knife blade that blocks light from the supply cassette and forms a border for the image projected onto the advanced web. Then a movable blade of the knife closes against the fixed blade to cut off the imaged sheet, which drops by gravity into the paper processor.
Changing the size of the image and the cut-off sheet for the Thebault printer requires moving the optical axis of the projection system relative to the fixed knife blade, which acts as an image boundary and light lock for the unadvanced paper. The security of the light lock attained by the emulsion side of the paper web resting, without backup pressure, against the fixed knife blade is also problematic.
I have devised a printer that cuts off a variable length sheet from an advanced photographic paper web and then moves the cut-off sheet via a vacuum platen to center the sheet on the optical axis of a fixed projection printer. This allows variation in the length of the cut-off sheet simply by varying the drive distance of the paper advance and the vacuum platen, without moving the optical axis of the printer. I have also devised a light lock system that reliably blocks light from the unexposed paper behind the cut-off knife, while the cut-off sheet is imaged. This ensures that imaging light from the printer does not fog the leading region of a subsequent sheet.
In my printer, the light locking, sheet cut-off, and sheet advancing, imaging, and processing devices all cooperate to allow economical and reliable variation in cut-off sheet size and reliable light locking during sheet imaging. These advantages are especially important in a customer-operated printer that responds readily to requests for different sizes of prints.